Lowpass filter control apparatus, lowpass filter control method, and imaging apparatus

ABSTRACT

A lowpass filter control apparatus of the present disclosure includes a lowpass filter controller that causes lowpass characteristics of a variable lowpass filter disposed in an optical path of incoming light into an imaging element including phase-difference pixels and normal pixels to be different for an exposure period of the normal pixels and an exposure period of the phase-difference pixels.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/074,223, filed Jul. 31, 2018, which is anational stage entry of PCT/JP2017/001692, filed Jan. 19, 2017, andclaims the benefit of priority from prior Japanese Patent Application JP2016-048401, filed Mar. 11, 2016, the entire content of which is herebyincorporated by reference. Each of the above-referenced applications ishereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a lowpass filter control apparatus, alowpass filter control method, and an imaging apparatus that are appliedto shooting with use of a variable lowpass filter.

BACKGROUND ART

Typically, compact cameras and mirrorless cameras adopt contrast systemautofocus (contrast AF). In contrast, in order to achieve high-speedautofocus, there is proposed phase-difference system autofocus(phase-difference AF) in which pixels for phase-difference detection(phase-difference pixel) are embedded in an imaging element.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2013-190603

PTL 2: Japanese Unexamined Patent Application Publication No. H05-048951

SUMMARY OF THE INVENTION

In a case where the phase-difference AF is adopted, the number ofembedded phase-difference pixels is limited in order not to deterioratequality of a shot image by an influence of the embedded phase-differencepixels. Hence, in particular, in focus detection of a high-frequencysubject, etc., detection data of a sufficient sampling number isobtained, which may cause an error in focus detection in some cases.

It is desirable to provide a lowpass filter control apparatus, a lowpassfilter control method, and an imaging apparatus that are allowed forhigh-accuracy focus detection.

A lowpass filter control apparatus according to an embodiment of thepresent disclosure includes a lowpass filter controller that causeslowpass characteristics of a variable lowpass filter disposed in anoptical path of incoming light into an imaging element includingphase-difference pixels and normal pixels to be different for anexposure period of the normal pixels and an exposure period of thephase-difference pixels.

A lowpass filter control method according to an embodiment of thepresent disclosure includes causing lowpass characteristics of avariable lowpass filter disposed in an optical path of incoming lightinto an imaging element including phase-difference pixels and normalpixels to be different for an exposure period of the normal pixels andan exposure period of the phase-difference pixels.

An imaging apparatus according to an embodiment of the presentdisclosure includes an imaging element including phase-difference pixelsand normal pixels; a variable lowpass filter disposed in an optical pathof incoming light into the imaging element; and a lowpass filtercontroller that causes lowpass characteristics of the variable lowpassfilter to be different for an exposure period of the normal pixels andan exposure period of the phase-difference pixels.

In the lowpass filter control apparatus, the lowpass filter controlmethod, or the imaging apparatus according to the embodiment of thepresent disclosure, the variable lowpass filter is controlled to causethe lowpass characteristics to be different for the exposure period ofthe normal pixels and the exposure period of the phase-differencepixels.

According to the lowpass filter control apparatus, the lowpass filtercontrol method, or the imaging apparatus according to the embodiment ofthe present disclosure, the variable lowpass filter is controlled tocause the lowpass characteristics to be different for the exposureperiod of the normal pixels and the exposure period of thephase-difference pixels, which makes it possible to performhigh-accuracy focus detection.

It is to be noted that effects described here are not necessarilylimited and may include any of effects described in the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an outline of an imaging apparatusaccording to a first embodiment of the present disclosure.

FIG. 2 is a block diagram illustrating a configuration example of acontrol system of the imaging apparatus.

FIG. 3 is a top view of a configuration example of a phase-differencepixel.

FIG. 4 is a cross-sectional view of a configuration example of thephase-difference pixel.

FIG. 5 is a configuration diagram illustrating a pixel structureincluding the phase-difference pixels.

FIG. 6 is an explanatory diagram illustrating a first example of anideal output value and a reproduced output value of the phase-differencepixels in a case where a variable lowpass filter does not reducehigh-frequency components.

FIG. 7 is an explanatory diagram illustrating a first example of theideal output value and the reproduced output value of thephase-difference pixels in a case where the variable lowpass filterreduces high-frequency components.

FIG. 8 is an explanatory diagram illustrating a second example of theideal output value and the reproduced output value of thephase-difference pixels in the case where the variable lowpass filterdoes not reduce high-frequency components.

FIG. 9 is an explanatory diagram illustrating a second example of theideal output value and the reproduced output value of thephase-difference pixels in the case where the variable lowpass filterreduces high-frequency components.

FIG. 10 is a flow chart illustrating an example of an operation ofcontrolling a cut frequency of the variable lowpass filter.

FIG. 11 is a flow chart illustrating an example of the operation ofcontrolling the cut frequency of the variable lowpass filter.

FIG. 12 is a flow chart illustrating an example of the operation ofcontrolling the cut frequency of the variable lowpass filter.

FIG. 13 is a flow chart illustrating an example of the operation ofcontrolling the cut frequency of the variable lowpass filter.

FIG. 14 is a flow chart illustrating an example of the operation ofcontrolling the cut frequency of the variable lowpass filter.

FIG. 15 is a flow chart illustrating an example of the operation ofcontrolling the cut frequency of the variable lowpass filter.

FIG. 16 is a flow chart illustrating an example of an operation ofcompositely controlling the cut frequency of the variable lowpassfilter.

FIG. 17 is an explanatory diagram illustrating an example of the cutfrequency of the variable lowpass filter.

FIG. 18 is a sequence diagram illustrating a sequence example in a caseof setting to a cut frequency for phase-difference AF.

MODES FOR CARRYING OUT THE INVENTION

In the following, some embodiments of the present disclosure aredescribed in detail with reference to the drawings. It is to be notedthat description is given in the following order.

1. First Embodiment

1.1 Configuration Example of Imaging Apparatus (FIGS. 1 and 2)

1.2 Configuration and Principle of Phase-difference Pixel (FIGS. 3 to 5)

1.3 Specific Examples of Control Operation of Variable Lowpass Filter(FIGS. 6 to 18)

1.4 Effects

2. Other Embodiments

1. First Embodiment

In a case where phase-difference AF is adopted, the number of embeddedphase-difference pixels is limited in order not to deteriorate qualityof a shot image by an influence of the embedded phase-difference pixels.Hence, in particular, in focus detection of a high-frequency subject,etc., detection data of a sufficient sampling number is obtained, whichmay cause an error in focus detection in some cases. In contrast, insome digital cameras, in order to reduce a component of a specific orhigher frequency of incoming light, an optical lowpass filter isdisposed in front of an imaging element to reduce a moiré phenomenon.Moreover, there is proposed a technique of allowing for change of afrequency to be reduced by the optical lowpass filter and setting, forexample, an optimum frequency for each of an all-pixel readout mode suchas a still image and a readout mode, in which addition or thinning ofpixels is performed, such as a moving image (e.g. PTL 1). Moreover, inorder to eliminate deterioration in focus detection accuracy specific toa contrast AF system that occurs in a case where the optical lowpassfilter is provided in front of a taking lens, there is also proposed atechnique of rotating the optical lowpass filter to make a cutofffrequency variable (e.g. PTL 2).

These existing technologies are techniques to reduce moiré of an imageand solve issues specific to the contrast AF system. Accordingly, forexample, there is proposed a control method in which whilehigh-frequency components are reduced by the optical lowpass filter uponnormal shooting to reduce moiré, the high-frequency components areprevented from being reduced upon focus detection. However, in a casewhere upon phase-difference system focus detection, control is performednot to reduce the high-frequency components, focus detection accuracy isdeteriorated by contraries by a limit to the number of embeddedphase-difference detection pixels as described above.

The present embodiment therefore provide an imaging apparatus allowingfor high-accuracy focus detection.

[1.1 Configuration Example of Imaging Apparatus]

(Outline of Imaging Apparatus)

FIG. 1 illustrates an outline of an imaging apparatus according to afirst embodiment of the present disclosure.

The imaging apparatus according to the present embodiment includes alens unit 1 and a camera body on which the lens unit 1 is mounted. Thecamera body includes an electronic viewfinder (EVF) 2, a variablelowpass filter (LPF) 3, an imaging element 4, and a liquid crystaldisplay unit 5.

The lens unit 1 forms an optical image of a subject on the imagingelement 4. The lens unit 1 includes a focus lens for focusing.

The imaging element 4 includes a CCD (Charge Coupled Device) sensor, aCMOS (Complementary Metal Oxide Semiconductor) sensor, or the like. Theimaging element 4 performs photoelectric conversion and A/D(analog-to-digital) conversion on the optical image formed by the lensunit 1 to output an imaging signal corresponding to the optical image.The imaging element 4 includes pixels 10 and phase-difference pixels 20,as illustrated in FIGS. 3 to 5 to be described later. Thephase-difference pixels 20 are pixels used to perform focus detection bythe phase-difference system. The pixels 10 are normal pixels used togenerate a shot image of the subject.

The variable lowpass filter 3 is disposed in front of the imagingelement 4 in an optical path of incoming light into the imaging element4. The variable lowpass filter 3 has a variable cut frequency as one oflowpass characteristics, and reduces a component of a frequencyexceeding the cut frequency of the incoming light into the imagingelement 4.

As the variable lowpass filter 3, it is possible to use, for example, avariable optical lowpass filter (OLPF) in which the lowpasscharacteristics are changed by controlling a degree of light separationof the incoming light. The variable optical lowpass filter includes, forexample, a first birefringent plate and a second birefringent plate, aliquid crystal layer, and a first electrode and a second electrode, andhas a configuration in which the liquid crystal layer is interposedbetween the first electrode and the second electrode, and is furtherinterposed between the first birefringent plate and the secondbirefringent plate from the outside thereof. In the variable opticallowpass filter, it is possible to control a polarization state of lightto continuously change the lowpass characteristics and change the cutfrequency. In the variable optical lowpass filter, changing an electricfield to be applied to the liquid crystal layer (a voltage appliedbetween the first electrode and the second electrode) makes it possibleto control the lowpass characteristics.

(Configuration of Control System of Imaging Apparatus)

FIG. 2 illustrates a configuration example of a control system of theimaging apparatus.

The imaging apparatus includes a memory 7, a lens driving controller 11,an imaging unit 41, a main controller 42, an imaging controller 43, avariable lowpass filter controller 44, a signal processor 45, an imageprocessor 46, a focus controller 47, a phase-difference focus detector48, and an operation unit 50.

The imaging unit 41 includes the above-described imaging element 4. Theimage processor 46 includes a contrast focus detector 49. The imageprocessor 46 may be coupled to an external monitor 6. The operation unit50 includes a main switch (main SW) 51 and a shutter button 52. Theshutter button 52 is also called release button.

The imaging apparatus according to the present embodiment has a manualfocus mode and an autofocus (AF) mode as focusing modes. The autofocusmode has a phase-difference AF mode and a contrast AF mode. Moreover,the autofocus mode may have a hybrid AF mode that is a combination ofphase-difference AF and contrast AF. Focus detection in thephase-difference AF mode is performed in the phase-difference focusdetector 48. Focus detection in the contrast AF mode is performed in thecontrast focus detector 49.

Moreover, the imaging apparatus according to the present embodiment hasa single AF mode and a continuous AF mode. In the single AF mode, afocus (a focal position) is fixed after focusing, and in the continuousAF mode, the focal position is continuously tracked in accordance withmovement of a subject.

Further, the imaging apparatus according to the present embodiment has alive view mode (LV mode) in which a shot image is displayed on theliquid crystal display unit 5 or the external monitor 6. Furthermore,the imaging apparatus has a magnified display mode in which the shotimage is magnified and displayed in the live view mode. For example, theimaging apparatus is set to the magnified display mode, for example, ina focus magnification mode or in a monitor output mode. In the focusmagnification mode, the shot image is magnified and displayed forfocusing, and in the monitor output mode, the shot image is displayed onthe external monitor 6.

(Outline of Operation of Imaging Apparatus)

In the imaging apparatus according to the present embodiment, the maincontroller 42 controls operation timings of various controllers. In acase where the main switch 51 is turned on to start a shootingoperation, an instruction of the live view mode is provided from theimaging controller 43 to the imaging unit 41, and an image signal forthe live view mode is transmitted to the signal processor 45.

The signal processor 45 separates the image signal for the live viewmode and a signal for phase-difference detection. The signal processor45 outputs the signal for phase-difference detection to thephase-difference focus detector 48. In the phase-difference focusdetector 48, a phase-difference detection value is calculated on thebasis of the signal for phase-difference detection, and is transmittedto the focus controller 47.

In contrast, the image signal for the live view mode is outputted to theimage processor 46. In the image processor 46, the contrast focusdetector 49 performs focus detection calculation by the contrast systemon the basis of the image signal, and a thus-obtained contrast detectionvalue is transmitted to the focus controller 47.

Thereafter, in a case where a focus detection operation is started by ahalfway press operation of the shutter button 52, etc., the focuscontroller 47 calculates a final focus adjustment control amount withuse of the phase-difference detection value and the contrast detectionvalue, and transmits a thus-obtained result to the lens drivingcontroller 11. For calculation of the focus adjustment control amount bythe focus controller 47, lens data 12 of the lens unit 1 is referred toas appropriate. The lens driving controller 11 causes the focus lens ofthe lens unit 1 to operate on the basis of the focus adjustment controlamount. Thus, a focus adjustment operation (autofocus operation) isperformed.

Thereafter, in a case where a shooting operation is started by afull-press operation of the shutter button 52, an instruction of a shotimage mode is provided from the imaging controller 43, and a signal forthe shot image is transmitted to the signal processor 45. Thus, the shotimage is generated. Data of the generated shot image is converted into apredetermined image format by the image processor 46, and is stored inthe memory 7 or an unillustrated external memory.

In contrast, the variable lowpass filter controller 44 controls the cutfrequency of the variable lowpass filter 3. The main controller 42 isallowed to control the cut frequency of the variable lowpass filter 3through the variable lowpass filter controller 44 in accordance withvarious setting states and various shooting states so as to allow forachievement of a lowpass effect suitable for the shot image or the focusdetection.

It is to be noted that the configuration example in FIG. 2 involves anexample in which various kinds of signal processing are performed in ablock different from the imaging unit 41. Alternatively, some or all ofthe various kinds of signal processing may be performed in the imagingunit 41. For example, a portion or the entirety of the signal processor45, the image processor 46, and the phase-difference focus detector 48may be modularized and integrated in the imaging unit 41.

[1.2 Configuration and Principle of Phase-difference Pixel]

FIGS. 3 and 4 illustrate a configuration example of the phase-differencepixel 20 embedded in the imaging element 4. FIG. 3 illustrates theconfiguration example of the phase-difference pixel 20 as viewed fromabove. FIG. 4 illustrates a cross-sectional configuration example of thephase-difference pixel 20.

The phase-difference pixels 20 includes a pair of phase-differencepixels 20A and 20B. The pair of phase-difference pixels 20A and 20B eachinclude a photodiode 24 and a filter unit that limits incoming lightinto the photodiode 24. The filter unit includes a light-shielding film21, a transmission unit 22, and a microlens 23.

In each of the pair of phase-difference pixels 20A and 20B, about a halfof the incoming light into the photodiode 24 is shielded by thelight-shielding film 21. Rays having different angles of the incominglight are detected by the photodiodes 24 of the pair of respectivephase-difference pixels 20A and 20B. Thus, a pupil region in themicrolens 23 is divided to allow light to enter one phase-differencepixel 20A and the other phase-difference pixel 20B at symmetric angles.As a result, a received light amount distribution of one pixel group ofthe phase-difference pixels 20A and a received light amount distributionof another pixel group of the phase-difference pixels 20B are deviatedin light amount distribution position from each other. A deviationamount between these received light amount distributions is a valuecorresponding to a deviation amount of a focal point in an optical axisdirection. Accordingly, the deviation amount between the received lightamount distributions is detected as a phase difference to determine thedeviation amount of the focal point in the optical axis direction.

FIG. 5 illustrates an entire configuration example of the pixel 10 inthe imaging element 4.

The pixels 10 of the imaging element 4 have, for example, a codingpattern called Bayer pattern. The pixels 10 include pixels of threecolors R (red), G (green), and B (blue) that are two-dimensionallyarranged and are different in position from one another. It is to benoted that in FIG. 5, the pixel of the color B is referred to Br. It isto be noted that in FIG. 5, the Bayer pattern is exemplified as a pixelstructure; however, the pixel structure may be any structure other thanthe Bayer pattern. Moreover, the pixels 10 may include pixels other thanR, G, and B. For example, the pixels 10 may further include a W (white)pixel.

Herein, in a case where the phase-difference pixels 20 are embedded inthe imaging element 4, it is necessary to determine shooting pixelvalues at positions where the phase-difference pixels 20 are embedded,by estimation from pixel values at any other pixel positions bycomplementing processing, etc. Accordingly, while focus detectionaccuracy is improved more with an increasing number of phase-differencepixels 20 embedded in the imaging element 4, the pixel number ofphase-difference pixels 20 is limited in order not to affect imagequality of the shot image. Hence, in actuality, the phase-differencepixels 20 are embedded in the imaging element 4 at suitable intervals asillustrated in FIG. 5 so as to appropriately perform the complementingprocessing by the pixels 10 around the phase-difference pixels 20 uponobtaining the shot pixel value.

(Example 1 of Output Value of Phase-difference Pixel 20 and Effect ofVariable Lowpass Filter 3)

FIG. 6 illustrates a first example of an ideal output value and areproduced output value of the phase-difference pixels 20 in a casewhere the variable lowpass filter 3 does not reduce high-frequencycomponents. FIG. 6 illustrates an example of an output value in a casewhere focus detection is performed on a monochrome single-edge subjectby the phase-difference pixel 20.

On a left side of FIG. 6, 60A indicates an output (an ideal value) byone pixel group of the phase-difference pixels 20A, and 60B indicates anoutput (an ideal value) by another pixel group of the phase-differencepixels 20B. These ideal outputs are outputs of optical images (an Aimage and a B image) in phase-difference pixels 20A and 20B in a casewhere it is assumed that an infinity number of the phase-differencepixels 20A and 20B are embedded. Pa and Pb are sampling points whereactual outputs are obtained in the phase-difference pixels 20A and 20B.Pa indicates a sampling point by the one phase-difference pixel 20A, andPb indicates a sampling point by the other phase-difference pixel 20B.

In actuality, the phase-difference pixels 20A and 20B are disposed atintervals; therefore, the outputs are obtainable only at the samplingpoints Pa and Pb. A right side of FIG. 6 illustrates an example in whichan output of a phase difference is reproduced on the basis of theoutputs from the sampling points Pa and Pb on the left side of FIG. 6.61A indicates an output (a reproduced value) by the one phase-differencepixel 20A, and 61 B indicates an output (a reproduced value) by theother phase-difference pixel 20B. As illustrated on the right side ofFIG. 6, in a case where a phase difference is reproduced only by theoutputs from the sampling points Pa and Pb, the phase difference has adifferent value from an intrinsic phase difference illustrated on theleft side of FIG. 6. Hence, performing focus detection on the basis ofthis phase difference causes a focus detection error.

As described above, in a case where the phase-difference pixels 20 areembedded at intervals in the imaging element 4, a focus detection errormay occur in some cases. As illustrated in FIG. 7, it is possible toreduce the focus detection error by setting the cut frequency of thevariable lowpass filter 3 to reduce frequency components suitable forarrangement of the phase-difference pixels 20, thereby allowing forphase-difference detection with high accuracy.

FIG. 7 illustrates a first example of the ideal output value and thereproduced output value of the phase-difference pixels 20 in a casewhere the variable lowpass filter 3 reduces the high-frequencycomponents. FIG. 7 illustrates an example of an output value in a casewhere focus detection is performed on a monochrome single-edge subjectby the phase-difference pixels 20, as with FIG. 6.

On a left side of FIG. 7, the output (the ideal value) 60A by the onepixel group of the phase-difference pixels 20 and the output (the idealvalue) by another pixel group of the phase-difference pixels 20B areillustrated, as with the left side of FIG. 6. Moreover, Pa and Pb aresampling points where actual outputs are obtained in thephase-difference pixels 20A and 20B.

A right side of FIG. 7 illustrates an example in which an output of aphase difference is reproduced on the basis of the outputs from thesampling points Pa and Pb on the left side of FIG. 7. 61A indicates anoutput (a reproduced value) by the one phase-difference pixel 20A, and61 B indicates an output (a reproduced value) by the otherphase-difference pixel 20B.

As can be seen from FIG. 7, even in a case where the variable lowpassfilter 3 reduces the high-frequency components to reproduce the phasedifference only by the outputs from the sampling points Pa and Pb, it ispossible to obtain a value close to the intrinsic phase differenceillustrated on the left side of FIG. 7. Hence, performing focusdetection on the basis of this phase difference reduces the focusdetection error.

(Example 2 of Output Value of Phase-difference Pixel 20 and Effect ofVariable Lowpass Filter 3)

FIG. 8 illustrates a second example of the ideal output value and thereproduced output value of the phase-difference pixels 20 in the casewhere the variable lowpass filter 3 does not reduce high-frequencycomponents. FIG. 9 illustrates a second example of the ideal outputvalue and the reproduced output value of the phase-difference pixels 20in the case where the variable lowpass filter 3 reduces thehigh-frequency components.

FIGS. 8 and 9 illustrate an example of an output value in a case wherefocus detection is performed on a subject having many high-frequencycomponents by the phase-difference pixels 20.

On a left side of FIG. 8, the output (the ideal value) 60A by the onepixel group of the phase-difference pixels 20A and the output (the idealvalue) by another pixel group of the phase-difference pixels 20B areillustrated, as with the left side of FIG. 6. Moreover, Pa and Pb aresampling points where actual outputs are obtained in thephase-difference pixels 20A and 20B.

A right side of FIG. 8 illustrates an example in which an output of aphase difference is reproduced on the basis of the outputs from thesampling points Pa and Pb on the left side of FIG. 8. 61A indicates anoutput (a reproduced value) by the one phase-difference pixel 20A, and61 B indicates an output (a reproduced value) by the otherphase-difference pixel 20B.

In a case where a phase difference with respect to the subject havingmany high-frequency components is reproduced only by the outputs fromthe sampling points Pa and Pb, not only a phase difference error islarge, but also it is not possible to reproduce an intrinsic phasedifference, which may make the phase-difference detection inexecutablein some cases. Hence, performing focus detection on the basis of thephase difference causes a large focus detection error or a case wherefocus detection is made inexecutable.

A left side of FIG. 9 illustrates the output (the ideal value) 60A bythe one pixel group of the phase-difference pixels 20A and the output(the ideal value) by another pixel group of the phase-difference pixels20B, as with the left side of FIG. 6. Moreover, Pa and Pb are samplingpoints where actual outputs are obtained in the phase-difference pixels20A and 20B.

A right side of FIG. 9 illustrates an example in which an output of aphase difference is reproduced on the basis of the outputs from thesampling points Pa and Pb on the left side of FIG. 9. 61A indicates anoutput (a reproduced value) by the one phase-difference pixel 20A, and61 B indicates an output (a reproduced value) by the otherphase-difference pixel 20B.

As can be seen from FIG. 9, even in a case where the variable lowpassfilter 3 reduces the high-frequency components to reproduce the phasedifference only by the outputs from the sampling points Pa and Pb, it ispossible to obtain a value close to the intrinsic phase differenceillustrated on the left side of FIG. 9. Even with respect to the subjecthaving many high-frequency components, reducing the high-frequencycomponents by the variable lowpass filter 3 causes relatively highwaveform reproducibility, thereby making the phase-difference detectioneasy. Hence, performing focus detection on the basis of the phasedifference reduces the focus detection error.

[1.3 Specific Examples of Control Operation of Variable Lowpass Filter]

In the imaging apparatus according to the present embodiment, thevariable lowpass filter controller 44 follows an instruction by the maincontroller 42, and performs control of the lowpass characteristics ofthe variable lowpass filter 3 in accordance with various setting statesand various shooting states. For example, as the control of the lowpasscharacteristics, the following control of the cut frequency of thevariable lowpass filter 3 is performed. It is to be noted that in thefollowing, description is given with reference to FIGS. 10 to 15 asappropriate.

The variable lowpass filter controller 44 controls the variable lowpassfilter 3 so as to perform switching of the cut frequency betweenfrequencies that are different in a phase-difference detection operationby the phase-difference focus detector 48 and in a shooting operation.In this case, the variable lowpass filter 3 is preferably controlled tocause the cut frequency in the phase-difference detection operation tobe lower than that in the shooting operation. The shooting operationherein is an operation of generating an image on the basis of the pixels10 that are normal pixels, and includes an exposure period of the pixels10. Moreover, the phase-difference detection operation is a focusdetection operation by a phase-difference system on the basis of thephase-difference pixels 20, and includes an exposure period of thephase-difference pixels 20.

Moreover, the variable lowpass filter controller 44 may change the cutfrequency in accordance with a condition of the subject in thephase-difference detection operation.

For example, in the phase-difference detection operation, in a casewhere luminance of the subject is lower than predetermined luminance(step S105; Y), the variable lowpass filter controller 44 controls thevariable lowpass filter 3 to cause the cut frequency to be higher thanthat in a case where the subject has higher luminance than thepredetermined luminance (step S105; N), as illustrated in FIG. 14.Moreover, for example, in the phase-difference detection operation, in acase where contrast of the subject is lower than predetermined contrast(step S105; Y), the variable lowpass filter controller 44 controls thevariable lowpass filter 3 to cause the cut frequency to be higher thanthat in a case where the contrast of the subject is higher than thepredetermined contrast (step S105; N).

Further, for example, in the phase-difference detection operation, in acase where a value of a predetermined high-frequency component includedin the subject is higher than a predetermined value, the variablelowpass filter controller 44 controls the variable lowpass filter 3 tocause the cut frequency to be lower than that in a case where the valueof the predetermined high-frequency component is lower than thepredetermined value. Furthermore, for example, in the phase-differencedetection operation, in a case where a value of a predetermined strongedge component included in the subject is higher than a predeterminedvalue, the variable lowpass filter controller 44 controls the variablelowpass filter 3 to cause the cut frequency to be lower than that in acase where the value of the predetermined strong edge component is lowerthan the predetermined value.

Moreover, the variable lowpass filter controller 44 may change the cutfrequency in accordance with a deviation amount of a focal point in thephase-difference detection operation.

For example, in the phase-difference detection operation, in a casewhere the deviation amount of the focal point is within a predeterminedrange (close into focus) (step S106; Y), the variable lowpass filtercontroller 44 controls the variable lowpass filter 3 to cause the cutfrequency to be lower than that in a case where the deviation amount ofthe focal point is out of the predetermined range (step S106; N), asillustrated in FIG. 15.

Moreover, for example, in an operation by the manual focus mode (stepS103; Y), the variable lowpass filter controller 44 controls thevariable lowpass filter 3 to cause the cut frequency to be higher thanthat in an operation by the autofocus mode (step S103; N), asillustrated in FIG. 12.

Further, for example, the variable lowpass filter controller 44 maychange the cut frequency in accordance with a magnification of magnifieddisplay in the magnified display mode, as illustrated in FIG. 12. Forexample, the variable lowpass filter controller 44 controls the variablelowpass filter 3 to cause the cut frequency to be higher with anincrease in the magnification of magnified display in the focusmagnification mode, the monitor output mode, etc. (step S103; Y).

Furthermore, in the focus detection operation, in a case where thecontrast detection operation is performed by the contrast focus detector49, the variable lowpass filter controller 44 may control the variablelowpass filter 3 to cause the cut frequency to be higher than that in acase where the contrast detection operation is not performed.

Moreover, for example, the variable lowpass filter controller 44 maycontrol the variable lowpass filter 3 to cause the cut frequency to belower in the continuous AF mode (step S104; N) than in the single AFmode (step S104; Y), as illustrated in FIG. 13.

Further, in a case where shooting of a moving image is in progress, thevariable lowpass filter controller 44 may control the variable lowpassfilter 3 to cause the cut frequency to be lower than that in a casewhere shooting of a still image is in progress.

Furthermore, for example, in a case where shooting of a still image byturning on the shutter button 52 is in progress, the variable lowpassfilter controller 44 may control the variable lowpass filter 3 to causethe cut frequency to be higher than that in the AF mode or the LV mode,as illustrated in FIG. 11.

FIG. 16 illustrates an example of an operation of compositelycontrolling the cut frequency of the variable lowpass filter 3 (a cutfrequency setting operation). The above-described control of thevariable lowpass filter 3 illustrated in FIGS. 10 to 15 may becompositely performed as illustrated in FIG. 16. It is to be noted thata flow of composite control illustrated in FIG. 16 is an example, andrespective steps may be executed in order different from order in theexample illustrated in FIG. 16. Moreover, the composite control may beperformed in a combination different from a combination of respectivesteps illustrated in FIG. 16.

First, the main controller 42 determines whether or not shooting of amoving image is in progress (step S101). In a case where the maincontroller 42 determines that shooting of the moving image is inprogress (step S101; Y), the main controller 42 causes variable lowpassfilter controller 44 to set the cut frequency of the variable lowpassfilter 3 to a cut frequency (a frequency 1) suitable for an image ofshooting of the moving image (step S110). In shooting of the movingimage, addition processing or pixel thinning processing are frequentlyperformed; therefore, the cut frequency is desirably set to a lowerfrequency than that for an image of shooting of a still image. In orderto perform optimization for autofocus (phase-difference detection)during shooting of the moving image, the cut frequency is desirably setto a lower frequency; however, the cut frequency is set to a cutfrequency suitable for the image of shooting of the moving image inpreference to quality of a stored image.

In a case where the main controller 42 determines that shooting of themoving image is not in progress (step S101; N), the main controller 42next determines whether or not shooting of the still image by pressingthe shutter button to turn on the shutter button 52 is in progress (stepS102). In a case where the main controller 42 determines that shootingof the still image is in progress (step S102; Y), the main controller 42causes the variable lowpass filter controller 44 to set the cutfrequency of the variable lowpass filter 3 to a cut frequency (afrequency 2) suitable for an image of shooting of the still image (stepS109).

In a case where the main controller 42 determines that shooting of thestill image is not in progress (step S102; N), the main controller 42next determines whether or not the manual focus mode, the focusmagnification mode, or the monitor output mode is established (stepS103). In a case where the main controller 42 determines that one ofthese modes is established (step S103; Y), the main controller 42 causesthe variable lowpass filter controller 44 to set the cut frequency ofthe variable lowpass filter 3 to a cut frequency (a frequency 3)suitable for the live view mode (step S108). In the manual focus mode,the focus magnification mode, or the monitor output mode, a shot imageis magnified and displayed on the liquid crystal display unit 5 or theexternal monitor 6. Accordingly, in order to improve visibility of theimage, it is desirable to set the cut frequency slightly higher to leavethe high-frequency components. It is to be noted that, in FIG. 16, thecut frequency is set to the cut frequency (frequency 3) for the liveview mode in all of the manual focus mode, the focus magnification mode,and the monitor output mode; however, the cut frequency may be set toindividual optimum cut frequencies for the respective modes. This alsoapplies to the following flow.

In a case where the main controller 42 determines that none of themanual focus mode, the focus magnification mode, and the monitor outputmode is established (step S103; N), the main controller 42 nextdetermines whether or not the single AF mode is established (step S104).

Even a camera that performs focus detection by the phase-differencesystem may perform shooting in the hybrid AF mode using focus detectionby the phase-difference system and focus detection by the contrastsystem in some cases. In general, in the contrast AF, accuracy is high,but a focal position where the high-frequency component becomes highestis detected while moving a lens position. Accordingly, it takes time fordetection, and in some cases, detection may slow in a case where anout-of-focus amount is large. In order to solve this issue, combined usewith focus detection by the phase-difference detection achieveshigh-speed and high-accuracy autofocus. However, in the contrast AF, thehigh-frequency components are detected; therefore, it is desirable notto excessively reduce the high-frequency components, and in a single AFshooting mode, the cut frequency is set to the same cut frequency (thefrequency 3) as that in the live view mode (step S108). However, even inthe single AF mode, it is possible to sequentially switch the cutfrequency in a case where focus detection by the phase-difference systemis performed and in a case where focus detection by the contrast systemis performed.

In contrast, in a case where the single AF mode is not established (stepS104; N), the continuous AF mode in which the focal position iscontinuously tracked in accordance with movement of the subject isestablished. In this case, autofocus by phase-difference detection ismainly used in preference to detection speed; therefore, the maincontroller 42 causes the variable lowpass filter controller 44 tobasically set the variable lowpass filter controller 44 to an optimumcut frequency (a frequency 4) for phase-difference AF (step S107).

However, even in this case, in a case where focus detection is performedon a subject having less high-frequency components and having lowluminance and low contrast as the conditions of the subject (step S105;Y), the cut frequency is desirably set to a slightly higher cutfrequency (the frequency 3). The subject having low luminance and lowcontrast is considered advantageous in accuracy in a case where thefrequency is not cut. Alternatively, even setting the cut frequency tothe slightly higher cut frequency (the frequency 3) for any subjectother than the subject including the high-frequency components or thestrong edge components that causes an increase in detection error makesit possible to achieve similar effects.

Moreover, in a case where the deviation amount of the focal point is outof the predetermined range and the subject is out of focus (step S106;N), the subject includes many low-frequency components, and a focusdetection error resulting from the interval between the above-describedphase-difference pixels 20 is less likely to occur.

Accordingly, in a case where the deviation amount of the focal point isout of the predetermined range, it is desirable to set the cut frequencyto the slightly higher cut frequency (the frequency 3) to rather leavethe high-frequency components. Further, in a case where the subject isbrought close into focus (step S106; Y), it is preferable to set the cutfrequency to the cut frequency (the frequency 4) for phase-differenceAF.

It is also possible to determine the above switching of the cutfrequency in accordance with conditions of the subject by informationother than focus detection, for example, luminance information and imageinformation of the subject, and it is possible to estimate the switchingfrom past focus detection information.

FIG. 17 illustrates an example of a relative relationship of thefrequencies 1 to 4 illustrated in the example in FIG. 16.

As illustrated in FIG. 17, (the frequency 4)<(the frequency 3)<(thefrequency 1)<(the frequency 2) is preferably set in increasing order ofthe cut frequency.

(Sequence Example)

FIG. 18 illustrates a sequence example in a case of setting to the cutfrequency (the frequency 4) for phase-difference AF in the flow in FIG.16.

First, when the main switch 51 is turned on, exposure and readout startto display an image on the liquid crystal display unit 5 (live viewdisplay). Thereafter, upon start of the focus detection operation by ahalfway press operation of the shutter button 5, phase-difference focusdetection by output of the phase-difference pixels 20 is performed afterexposure and readout to start a phase-difference AF operation. At thistime, the variable lowpass filter 3 is optically set forphase-difference detection. A user determines composition of thesubject, and presses the shutter button 52 to start the shootingoperation; however, at this time, in the imaging apparatus, diaphragmcontrol is performed to perform exposure of an image for shooting.Before the exposure starts, the main controller 42 performs control tocause the variable lowpass filter controller 44 to set the cut frequencyof the variable lowpass filter 3 to a cut frequency suitable for a shotimage. Thereafter, readout of image data and writing to the memory 7 areperformed. However, after the exposure is completed, for a next focusdetection operation, the cut frequency is returned to the cut frequencyfor phase-difference focus detection. It is to be noted that in a casewhere the mode is set to a continuous shooting mode or the like tocontinuously perform exposure and readout, the main controller 42 causesthe variable lowpass filter controller 44 to set the cut frequency ofthe variable lowpass filter 3 to a cut frequency for the shot image.

[1.4 Effects]

As described above, according to the present embodiment, the lowpasscharacteristics of the variable lowpass filter 3 are caused to bedifferent for the exposure period of the pixels 10 that are normalpixels and the exposure period of the phase-difference pixels 20, whichmakes it possible to perform high-accuracy focus detection.

According to the present embodiment, in a case where phase-differencefocus detection is performed, the cut frequency of the variable lowpassfilter 3 is set to a frequency suitable for the phase differencedetection so as to reduce a focus detection error, which makes itpossible to perform high-accuracy focus detection.

It is to be noted that the effects described in the description aremerely illustrative and non-limiting, and other effects may be included.This applies to effects achieved by the following other embodiments.

2. Other Embodiments

The technology achieved by present disclosure is not limited todescription of the above-described respective embodiments, and may bemodified in a variety of ways.

For example, the variable lowpass filter 3 is not limited to the opticalvariable lowpass filter, and may have any other configuration. Forexample, a piezoelectric device may be used to minutely vibrate theimaging element 4, thereby achieving a lowpass filter effect.Alternatively, the lowpass filter effect may be achieved by moving atleast some lenses of the lens unit 1.

Moreover, various forms are conceivable as variations of a camera towhich the imaging apparatus illustrated in FIG. 1 is applied. The lensunit 1 may be of a fixed type or an interchangeable type. In a casewhere the lens unit 1 is of the interchangeable type, the variablelowpass filter 3 may be provided not in the camera body but in the lensunit 1.

Further, the technology achieved by the present disclosure is applicableto an in-vehicle camera, a surveillance camera, etc. In addition, thetechnology achieved by the present disclosure is applicable to a camerafor medical use such as an endoscope.

Furthermore, in the imaging apparatus illustrated in FIG. 1, a shootingresult may be stored in the memory 7 or an external memory, or theshooting result may be displayed on the liquid crystal display unit 5;however, image data may be transmitted to any other device through anetwork, in place of being stored or displayed. Moreover, the signalprocessor 45, the image processor 46, the variable lowpass filtercontroller 44, etc. may be separated from a main body of the imagingapparatus. For example, these processors may be provided at an end of anetwork coupled to the imaging apparatus. Further, the main body of theimaging apparatus may store image data in an external memory withoutperforming image processing, etc., and may cause a different device suchas a PC (personal computer) to perform image processing.

It is to be noted that processing by the signal processor 45, the imageprocessor 46, the variable lowpass filter controller 44, etc. may beexecuted as a program by a computer. A program of the present disclosureis, for example, a program provided from, for example, a storage mediumto an information processing device and a computer system that areallowed to execute various program codes. Executing such a program bythe information processing device or a program execution unit in thecomputer system makes it possible to achieve processing corresponding tothe program.

Moreover, a series of image processing and control processing by thepresent technology may be executed by hardware, software, or acombination thereof. In a case where processing by software is executed,it is possible to install a program holding a processing sequence in amemory in a computer that is built in dedicated hardware, and cause thecomputer to execute the program, or it is possible to install theprogram in a general-purpose computer that is allowed to execute variouskinds of processing, and cause the general-purpose computer to executethe program. For example, it is possible to store the program in thestorage medium in advance. In addition to installing the program fromthe storage medium to the computer, it is possible to receive theprogram through a network such as LAN (Local Area Network) and theInternet and install the program in a storage medium such as a built-inhard disk. Moreover, the present technology may have the followingconfigurations, for example.

(1)

A lowpass filter control apparatus, including:

a lowpass filter controller that causes lowpass characteristics of avariable lowpass filter disposed in an optical path of incoming lightinto an imaging element including phase-difference pixels and normalpixels to be different for an exposure period of the normal pixels andan exposure period of the phase-difference pixels.

(2)

The lowpass filter control apparatus according to (1), in which thelowpass filter controller controls the variable lowpass filter to causea cut frequency of the variable lowpass filter in the exposure period ofthe phase-difference pixels to be lower than the cut frequency in theexposure period of the normal pixels.

(3)

The lowpass filter control apparatus according to (1) or (2), in whichthe lowpass filter controller changes the lowpass characteristics inaccordance with a condition of a subject in the exposure period of thephase-difference pixels.

(4)

The lowpass filter control apparatus according to (3), in which in theexposure period of the phase-difference pixels, in a case whereluminance of the subject is lower than predetermined luminance or in acase where contrast of the subject is lower than predetermined contrast,the lowpass filter controller controls the variable lowpass filter tocause the cut frequency of the variable lowpass filter to be higher thanthe cut frequency in a case where the subject has higher luminance thanthe predetermined luminance or in a case where the subject has highercontrast than the predetermined contrast.

(5)

The lowpass filter control apparatus according to (3), in which in theexposure period of the phase-difference pixels, in a case where a valueof a predetermined high-frequency component included in the subject ishigher than a predetermined value or in a case where a value of apredetermined strong edge component included in the subject is higherthan a predetermined value, the lowpass filter controller controls thevariable lowpass filter to cause the cut frequency of the variablelowpass filter to be lower than the cut frequency in a case where thevalue of the predetermined high-frequency component is lower than thepredetermined value or in a case where the value of the predeterminedstrong edge component is lower than the predetermined value.

(6)

The lowpass filter control apparatus according to any one of (1) to (5),in which the lowpass filter controller changes the cut frequency of thevariable lowpass filter in accordance with a deviation amount of a focalpoint in a phase-difference detection operation by the phase-differencepixels.

(7)

The lowpass filter control apparatus according to (6), in which in thephase-difference detection operation by the phase-difference pixels, ina case where the deviation amount of the focal point is within apredetermined range, the lowpass filter controller controls the variablelowpass filter to cause the cut frequency to be lower than the cutfrequency in a case where the deviation amount of the focal point is outof the predetermined range.

(8)

The lowpass filter control apparatus according to any one of (1) to (7),in which in an operation by a manual focus mode, the lowpass filtercontroller controls the variable lowpass filter to cause a cut frequencyof the variable lowpass filter to be higher than the cut frequency in anoperation by an autofocus mode.

(9)

The lowpass filter control apparatus according to any one of (1) to (8),in which the lowpass filter controller changes a cut frequency of thevariable lowpass filter in accordance with a magnification of magnifieddisplay in a magnified display mode in which a shot image by the normalpixels is magnified and displayed.

(10)

The lowpass filter control apparatus according to (9), in which thelowpass filter controller controls the variable lowpass filter toincrease the cut frequency with an increase in the magnification of themagnified display.

(11)

The lowpass filter control apparatus according to any one of (1) to(10), in which in a focus detection operation, in a case where adetection operation by a contrast system is performed, the lowpassfilter controller controls the variable lowpass filter to cause a cutfrequency of the variable lowpass filter to be higher than the cutfrequency in a case where the detection operation by the contrast systemis not performed.

(12)

The lowpass filter control apparatus according to any one of (1) to(11), in which in a continuous autofocus mode in which a focal positionis continuously tracked in accordance with movement of a subject, thelowpass filter controller controls the variable lowpass filter to causea cut frequency of the variable lowpass filter to be lower than the cutfrequency in a single autofocus mode in which the focal position isfixed after focusing.

(13)

A lowpass filter control method, including:

causing lowpass characteristics of a variable lowpass filter disposed inan optical path of incoming light into an imaging element includingphase-difference pixels and normal pixels to be different for anexposure period of the normal pixels and an exposure period of thephase-difference pixels.

(14)

An imaging apparatus, including:

an imaging element including phase-difference pixels and normal pixels;

a variable lowpass filter disposed in an optical path of incoming lightinto the imaging element; and

a lowpass filter controller that causes lowpass characteristics of thevariable lowpass filter to be different for an exposure period of thenormal pixels and an exposure period of the phase-difference pixels.

This application claims the benefit of Japanese Priority PatentApplication No. 2016-048401 filed with the Japan Patent Office on Mar.11, 2016, the entire contents of which are incorporated herein byreference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A lowpass filter control apparatus, comprising: a lowpass filter controller configured to: control lowpass characteristics of a variable lowpass filter, wherein the variable lowpass filter is in an optical path of light that enters an imaging element, and the imaging element includes a plurality of phase-difference pixels and a plurality of normal pixels; and change a first cut frequency of the variable lowpass filter based on a magnification of a magnified display in a magnified display mode of an imaging device, wherein the magnified display mode is a mode in which a shot image by the plurality of normal pixels is magnified and displayed on a display device.
 2. The lowpass filter control apparatus according to claim 1, wherein the lowpass filter controller is further configured to control the variable lowpass filter to increase the first cut frequency of the variable lowpass filter with an increase in the magnification of the magnified display.
 3. The lowpass filter control apparatus according to claim 1, wherein the lowpass filter controller is further configured to: set a second cut frequency of the variable lowpass filter for an exposure period of the plurality of phase-difference pixels; and set a third cut frequency of the variable lowpass filter for an exposure period of the plurality of normal pixels, wherein the second cut frequency is lower than the third cut frequency.
 4. The lowpass filter control apparatus according to claim 1, wherein the lowpass filter controller is further configured to change the lowpass characteristics of the variable lowpass filter based on a condition of a subject in an exposure period of the plurality of phase-difference pixels.
 5. The lowpass filter control apparatus according to claim 4, wherein in the exposure period of the plurality of phase-difference pixels, the lowpass filter controller is further configured to control the variable lowpass filter to: set a second cut frequency of the variable lowpass filter in a case where the subject has one of a luminance lower than a specific luminance or a contrast lower than a specific contrast; and set a third cut frequency of the variable lowpass filter in a case where one of the luminance of the subject is higher than the specific luminance or the contrast of the subject is higher than the specific contrast, and the second cut frequency is higher than the third cut frequency.
 6. The lowpass filter control apparatus according to claim 4, wherein in the exposure period of the plurality of phase-difference pixels, the lowpass filter controller is further configured to control the variable lowpass filter to: set a second cut frequency of the variable lowpass filter in a case where the subject has one of a first value of a high-frequency component higher than a first specific value or a second value of a strong edge component higher than a second specific value; and set a third cut frequency of the variable lowpass filter in a case where one of the first value of the high-frequency component is lower than the first specific value or the second value of the strong edge component is lower than the second specific value, and the second cut frequency is lower than the third cut frequency.
 7. The lowpass filter control apparatus according to claim 1, wherein the lowpass filter controller is further configured to change the first cut frequency of the variable lowpass filter based on a deviation amount of a focal point in a phase-difference detection operation by the plurality of phase-difference pixels.
 8. The lowpass filter control apparatus according to claim 7, wherein in the phase-difference detection operation by the plurality of phase-difference pixels, the lowpass filter controller is further configured to control the variable lowpass filter to: set a second cut frequency of the variable lowpass filter in a case where the deviation amount of the focal point is within a specific range; and set a third cut frequency of the variable lowpass filter in a case where the deviation amount of the focal point is out of the specific range, and the second cut frequency is lower than the third cut frequency.
 9. The lowpass filter control apparatus according to claim 1, wherein the lowpass filter controller is further configured to control the variable lowpass filter to: set a second cut frequency of the variable lowpass filter for an operation by a manual focus mode of an imaging device; and set a third cut frequency of the variable lowpass filter for an operation by an autofocus mode of the imaging device, and the second cut frequency is higher than the third cut frequency.
 10. The lowpass filter control apparatus according to claim 1, wherein in a focus detection operation of an imaging device, the lowpass filter controller is further configured to control the variable lowpass filter to: set a second cut frequency of the variable lowpass filter in a case where a detection operation is executed by a contrast system; and set a third cut frequency of the variable lowpass filter in a case where the detection operation is not executed by the contrast system, and the second cut frequency is higher than the third cut frequency.
 11. The lowpass filter control apparatus according to claim 1, wherein the lowpass filter controller is further configured to control the variable lowpass filter to: set a second cut frequency of the variable lowpass filter in a continuous autofocus mode in which a focal position is continuously tracked in association with movement of a subject; and set a third cut frequency of the variable lowpass filter in a single autofocus mode in which the focal position is fixed after a focus operation, wherein the second cut frequency is lower than the third cut frequency.
 12. A lowpass filter control method, comprising: controlling lowpass characteristics of a variable lowpass filter to change a cut frequency of the variable lowpass filter based on a magnification of a magnified display in a magnified display mode of an imaging device, wherein the magnified display mode is a mode in which a shot image by a plurality of normal pixels is magnified and displayed on a display device, the variable lowpass filter is in an optical path of light that enters an imaging element, and the imaging element includes a plurality of phase-difference pixels and the plurality of normal pixels.
 13. An imaging apparatus, comprising: an imaging element including a plurality of phase-difference pixels and a plurality of normal pixels; a variable lowpass filter in an optical path of light that enters the imaging element; and a lowpass filter controller configured to control lowpass characteristics of the variable lowpass filter to change a cut frequency of the variable lowpass filter based on a magnification of a magnified display in a magnified display mode of an imaging device, wherein the magnified display mode is a mode in which a shot image by the plurality of normal pixels is magnified and displayed on a display device. 